The present invention relates to a recordable and reproducible DVD-RAM (digital versatile disk-random access memory) disk reproduction apparatus, and more particularly, to a DVD-RAM disk apparatus for reducing errors during detection of identification (ID) data from a signal read from the DVD-RAM disk.
A recent form of a DVD is a DVD-RAM capable of recording and deleting data freely. Such a DVD-RAM disk has a recording capacity capable of recording massive amounts of data. The DVD-RAM disk comprises data sectors for use in recording data. Each data sector largely includes a header region and a recording region. The header region is divided into two sub-regions which are disposed adjacent to each other. Here, a region which is located in a relatively higher position is defined as an upper header region, and a region which is located in a relatively lower position is defined as a lower header region. The header region includes ID data containing a sector number and sector information. The recording region is called a user region which includes main data being information to be recorded.
FIG. 1 shows the structure of a general DVD-RAM disk reproduction apparatus. Referring to FIG. 1, the DVD-RAM disk reproduction apparatus includes an optical pickup 12 for reading signals from a DVD-RAM disk 11, and a playback signal amplifier 13 for amplifying signals read via the optical pickup 12. The DVD-RAM disk reproduction apparatus also includes an equalizer 14 for receiving a playback signal amplified in the playback signal amplifier 13 and equalizing the received signal for frequency characteristic compensation, a data detector 15 for producing a digital signal from the signal equalized in the equalizer 14, and a phase locked loop (PLL) 16 for synchronizing the output of the data detector 15 with a sync clock and outputting the synchronized result to a digital signal processor.
FIG. 2 is a detailed circuit diagram showing the playback signal amplifier 13 shown in FIG. 1. As shown in FIG. 2, the playback signal amplifier 13 includes a pair of operational amplifiers 21 and 22 for respectively obtaining a sum and a difference of four signals A, B, C and D picked up by divided-by-four photodiodes in the optical pickup 12, and a header region detector 23 for receiving the difference signal obtained by the operational amplifier 22 and detecting a header region of the DVD-RAM disk 11. The header region detector 23 includes an upper header region detector 231 and a lower header region detector 232 for respectively detecting an upper header region and a lower header region based on the input difference signal, and a logical sum unit (OR) 233 for logically summing signals of the detected upper and lower header regions. The playback signal amplifier 13 also includes a multiplexer RF MUX 24 for selecting the sum signal and difference signal obtained in the pair of the operational amplifiers 21 and 22 according to a result of the operation of the logical sum unit 233, and outputting the select result to the equalizer 14. The operation of the conventional DVD-RAM disk reproduction apparatus of FIGS. 1 and 2 having the above structure will be described in more detail with reference to FIGS. 3A through 3G.
As shown in FIG. 3A, the DVD-RAM disk 11 includes a header region and a recording region in each sector of a track, in which the header region comprises two portions of an upper header region and a lower header region. A signal read via the optical pickup 12 from the DVD-RAM disk 11 having such a track structure is processed via two paths in the playback signal amplifier 13.
Referring to FIG. 2, the first operational amplifier 21 of the playback signal amplifier 13 adds all four signals A, B, C and D picked up by the divided-by-four photodiodes in the optical pickup 12 and outputs a sum signal A+B+C+D as shown in FIG. 3B to the multiplexer 24. The second operational amplifier 22 obtains a push-pull signal and outputs a difference signal (A+B)xe2x88x92(C+D) as shown in FIG. 3C to the multiplexer 24, in which the latter added result is subtracted from the former added result. Here, the sum signal A+B+C+D is used in order to reproduce user data recorded in a recording region on a disk track, and the difference signal (A+B)xe2x88x92(C+D) is used in order to reproduce ID data in a header region thereof. Although the signal in the header region also appears in the sum signal A+B+C+D as shown in FIG. 3B, the characteristics of the signal appearing in the difference signal (A+B)xe2x88x92(C+D) as shown in FIG. 3C is better. Thus, the difference signal (A+B)xe2x88x92(C+D) of FIG. 3C is used for detection of the ID data in the header region. The upper header region detector 231 and the lower header region detector 232 in the header region detector 23 commonly receive the difference signal (A+B)xe2x88x92(C+D) shown in FIG. 3C obtained from the second operational amplifier 22 and detect the upper header region and the lower header region, respectively. Accordingly, the upper header region detector 231 and the lower header region detector 232 output the upper header region signal HD1 and the lower header region signal HD2 as shown in FIGS. 3D and 3E, respectively. That is, although not shown in the drawing, the upper header region detector 231 and the lower header region detector 232 include an envelope detector and a comparator, respectively. The upper header region detector 231 and the lower header region detector 232 each detect an envelope value from the difference signal (A+B)xe2x88x92(C+D) and compares the detected envelope value with a corresponding predetermined reference value, to thereby determine a portion corresponding to the upper header region and the lower header region. If the portion is determined as the upper header region or the lower header region, the corresponding upper header region detector 231 or the lower header region detector 232 outputs a high-level signal represented as a binary signal xe2x80x9c1xe2x80x9d and otherwise outputs a low-level signal represented as a binary signal xe2x80x9cOxe2x80x9d, as the upper header region signal and the lower header region signal as shown in FIGS. 3D and 3E, respectively. The logical sum unit 233 receives the upper and lower header region signals of HD1 and HD2 of FIGS. 3D and 3E detected in the upper header region detector 231 and the lower header region detector 232 and logically sums the received signals, to obtain a header region signal HD3 shown in FIG. 3F and outputs the same as a signal for controlling the multiplexer 24. The multiplexer 24 selectively outputs one of the sum signal A+B+C+D of FIG. 3B and the difference signal (A+B)xe2x88x92(C+D) of FIG. 3C to the equalizer 14 according to the header region signal HD shown in FIG. 3F applied from the logical sum unit 233 in the header region detector 23. That is, the multiplexer 24 selects the difference signal (A+B)xe2x88x92(C+D) of FIG. 3C during a high-level interval represented as a binary signal xe2x80x9c1xe2x80x9d of FIG. 3F, and selects the sum signal A+B+C+D of FIG. 3B during a low-level interval represented as a binary signal xe2x80x9c0xe2x80x9d, and outputs the selected signal as an RF signal. The equalizer 14 equalizes the RF signal selectively output from the multiplexer 24 in the playback signal amplifier 13 and then compensates for frequency characteristics, to thereby output the compensated result to the data detector 15. The data detector 15 detects data from the equalized signal and the PLL 16 restores the clock to be output to a digital signal processor.
As described above, the conventional DVD-RAM disk reproduction apparatus uses a difference signal (A+B)xe2x88x92(C+D) of the four signals picked up in the photodiodes in the optical pickup, in order to detect ID data of the header region on a DVD-RAM disk track.
Thus, considering the structure of the header region, signals should be picked up only at the divided-by-four photodiodes A and B during pickup of the upper header region, and signals should be picked up only at the divided-by-four photodiodes xe2x80x9cCxe2x80x9d and xe2x80x9cDxe2x80x9d during pickup of the lower header region. However, as shown in the waveform of the playback signal reproduced from the DVD-RAM disk in FIG. 6, a signal having a form of a sum signal (C+D) of the photodiodes C and D and not being a direct-current DC component appears in a portion xe2x80x9caxe2x80x9d of the photodiodes A+B during pickup of the lower head region. This is caused by inferiority of assembly of an optical system, interference between adjacent tracks, and inferiority of focus/tracking of a servo system. As a result, an amplitude characteristic of a signal portion xe2x80x9cbxe2x80x9d corresponding to the lower header region in the difference signal (A+B)xe2x88x92(C+D) between the two sum signals deteriorates, to thereby generate an error during detection of ID data.
To solve the above problems, it is an object of the present invention to provide a DVD-RAM disk reproduction apparatus for properly selecting two sum signals instead of a difference signal to be used for detection of ID data, in order to detect ID data of a header region more stably.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
A DVD-RAM disk reproduction apparatus for reducing errors during detection of ID data, the apparatus comprising a DVD-RAM disk having a plurality of data sectors each having a header region, which stores the ID data and includes an upper header region and a lower header region which are disposed adjacent to each other one on the skew top of the other, and a recording region which stores user data; an optical pickup to pick up a plurality of signals from the DVD-RAM disk; a playback signal amplifier which obtains a data signal for reproducing the user data which is recorded in the recording region of the DVD-RAM disk from the plurality of signals picked up from the disk via the optical pickup, obtains an ID signal for reproducing the ID data which is recorded in the header region using a control signal, divides the plurality of signals in correspondence to disposition of the upper header region and the lower header region in the header region to generate the control signal, and outputs the data and ID signals in correspondence to the recording region and the header region; and means for processing the data and ID signals output from the playback signal amplifier.